109
CHAPTER THREE
Cells
Death receptor on doomed cell
binds signal molecule. Caspases
are activated within.
Caspases destroy various
proteins and other cell components.
Cell becomes deformed.
Phagocyte attacks
and engulfs cell
remnants. Cell
components are
degraded.
Cell fragments
Blebs
sues and organs neither overgrow nor shrink. Disruptions in
either process can cause cancer.
PRACTICE
36
What is apoptosis?
37
List two general functions of apoptosis.
38
List the steps of apoptosis.
called
blebs
. The nucleus bursts under the multiple strains,
releasing same-sized DNA pieces. Mitochondria decompose.
Finally, the cell shatters. Almost instantly, pieces of membrane
encapsulate the fragments, which prevents the signaling that
triggers infl ammation. Within an hour of the ± rst release of
caspases, the cell that underwent apoptosis is gone.
Mitosis and apoptosis are synchronized throughout
development, maturation, and aging, and as a result, tis-
FIGURE 3.42
Death of a cell.
A cell undergoing apoptosis loses its
characteristic shape, forms blebs, and F
nally falls apart. Caspases destroy
the cell’s insides. Phagocytes digest the remains. Sunburn peeling is one
example of apoptosis.
3. Cell membrane
a. The cell membrane forms the outermost limit of
the living material.
b. It acts as a selectively permeable passageway that
controls the movements of substances between
the cell and its surroundings and thus is the site of
signal transduction.
c. It includes protein, lipid, and carbohydrate
molecules.
d. The cell membrane framework mainly consists of a
double layer of phospholipid molecules.
e. Molecules that are soluble in lipids pass through
the membrane easily, but water-soluble molecules
do not.
f. Cholesterol molecules help stabilize the
membrane.
CHAPTER SUMMARY
3.1
INTRODUCTION (PAGE 76)
1. Differentiated cells vary considerably in size, shape,
and function.
2. The shapes of cells are important in determining their
functions.
3. Specialized cells descend from less specialized cells.
3.2
A COMPOSITE CELL (PAGE 76)
1. A cell is a basic unit of an organism and includes a
nucleus, cytoplasm, and a cell membrane.
2. Cytoplasmic organelles perform speci±
c vital
functions, but the nucleus controls the overall
activities of the cell.
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